To "sniff the treat" means to take a quick smell of something that looks enticing or delicious, like a treat or snack, usually to determine its scent or flavor. Full definition
Your dog will stop straight away because he can't sniff the treat while barking; after a few seconds, give him the reward. (hillspet.hk)
I was suggested in a book that I should let the puppy sniff a treat, then raise the hand with the treat so that the puppy follows the hand by his eyes and when you raise the hand, your puppy will land his butt in the floor. (snowyswan.com)
Let the rabbit sniff the treat and put it into the toy with the bun watching. (myhouserabbit.com)